I do not think you need an install service as the application is already installed.
I am not really sure what you want me to do as far as an SSL warning. I answered the question posed here about the user posting in this thread about his photo url was not the ssl url and that is why he had to update his storage options.
Therefore your program looks like all the urls are right https://baeckerei-lieb.de/photopost/index.php https://www.baeckerei-lieb.de/photop...-suedback.html https://www.baeckerei-lieb.de/photop...ckforum-2.html
If I view anything in my browser on the gallery everything views fine so I see no problems.
As far as your CMS widget just make sure whatever hack your using that whatever path or coding your using does not have a double slash. Something like that is not supported code from us. Meaning it is not part of the photopost application.